Marijuana, widely used in the United States today, is consumed primarily by smoking. The pulmonary alveolar macrophage is the key host defense cell of the lung and has a crucial role in the pathogenesis of lung disease associated etiologically with inhalation of smoke from any source. Our studies will quantitatively define the biochemical, metabolic, enzymatic, ultrastructural and functional effects of marijuana on the lung and on the pulmonary alveolar macrophage both in vivo and in vitro. Emphasis will be placed on quantitative dosimetry studies and on an evaluation of the relationship between partitioned components of marijuana smoke and potential lung injury. Selected investigations will evaluate the biologic effects on the lung of tetrahydrocannabinol (THC) individually and in combination with other marijuana smoke components. If marijuana smoking represents a significant health hazard, these studies will help clarify that issue and provide objective data on the biologic effects of marijuana on pulmonary host defenses. Data of this nature are vitally needed for defining policies of marijuana use and for developing realistic legislation on scientific bases.